This invention relates to a communication system and a communication method for transmitting/receiving signals over a transmission line. More particularly, it relates to a communication system and a communication method employing multi-level modulation system.
The multi-level modulation system is used in particular in e.g., digital micro-wave communication. Heretofore, 2nQAM, such as 4QAM, 16QAM, 32QAM, 64QAM, 128QAM, 256QAM and so forth have been used in the multi-level modulation.
In the digital micro-wave communication, 4QAM, 16QAM, 32QAM, 64QAM, 128QAM, 256QAM and so forth have been used in general for circuit simplicity. However, with recent progress in the integrated circuit technology, implementation difficulties ascribable to circuit complexity are decreasing, while a demand for effective frequency utilization and effective transmission power utilization are becoming stronger.
For meeting with this demand, various methods for constructing the multi-level modulation system, in which the number of the multi-level is not necessarily 2n, have been proposed. Typical of these are xe2x80x9cMulti-Level Modulation Demodulation Communication Method and Systemxe2x80x9d as disclosed in the JP Patent Kokai Publication JP-A-04-196945, xe2x80x9cMulti-Level Modulation Demodulation Device, Multi-Level Modulation Demodulation Communication System, Modulation Demodulation Program and Modulation Demodulation Methodxe2x80x9d as disclosed in the JP Patent Application No. 2001-246891, not laid open as of the filing time of the present application, and xe2x80x9cMulti-Level Modulation Demodulation Device, Multi-Level Modulation Demodulation Communication System, Modulation Demodulation Program and Modulation Demodulation Methodxe2x80x9d as disclosed in the JP Patent Application No. 2001-246890, not laid open as of the filing time of the present application.
The above proposals are directed to the methods for constructing the multi-level modulation but not to the application of the multi-leveled error correction system. In consideration of error occurrence on the transmission line, it is mandatory to encode an information sequence into a transmit sequence and to decode the received sequence added with errors produced on the transmission line to obtain a decoded sequence. An error correction system is therefore required which is in coping with the degradation of signal quality on the multi-level modulation system.
The block diagram of FIG. 12 shows a correction system conforming to the multi-level modulation system which is thought to be routine among those skilled in the art. Referring to FIG. 12, a transmitting apparatus 901 of the related art includes a binary error correction encoding circuit 902, a binary to N-ary conversion circuit 903 and a multi-level modulation unit 904, while a receiving apparatus 921 of the related art includes a multi-level demodulation unit 922, an N-ary to binary conversion circuit 923 and a binary error correction decoding circuit 923. Neither the transmitting apparatus 901 nor the receiving apparatus 921 uses the nonbinary error correction system, which is based on the nonbinary error correction code. In the transmitting apparatus 901, the binary error correction coding circuit, generating the error correction code based on the binary signal, is placed ahead of the binary to N-ary conversion circuit 903, whereas, in the receiving apparatus 921, the binary error correction decoding circuit, carrying out the error correction based on the binary signal, is placed at back of the binary error correction decoding circuit 923.
However, with the configuration of FIG. 12, no efficient error correction system, for coping with the multi-level transmission, can be implemented. That is, the configuration of FIG. 12 leads to redundancy for achieving the equivalent code length which is larger than in case the nonbinary code is used.
In view of the above-depicted status of the art, it is an object of the present invention to provide a communication system and a communication method which includes an efficient error correction system and which is designed to transmit/receive an N-ary signal in which N is a prime number exceeding 2.
The above and other objects are attained by a communication system in accordance with one aspect of the present invention, including a transmitting apparatus and a receiving apparatus for sending/receiving signals over a transmission line, wherein the transmitting apparatus comprises binary to N-ary converting means for converting a binary transmit signal into an N-ary signal, as an information sequence, the N-ary number being a prime number exceeding 2, encoding means for generating a transmit sequence which includes a nonbinary error correction code, based on the N-ary signal as the information sequence, and multi-level modulating means for modulating the transmit sequence to send the modulated transmit sequence to the receiving apparatus, and wherein the receiving apparatus comprises demodulating means for demodulating the received signal sent from the transmitting apparatus and for producing a multi-leveled received sequence, the multi-level being a prime number exceeding 2, decoding means for decoding the received sequence by a nonbinary error correction code decoding method to produce an N-ary signal, the N-ary number being a prime number exceeding 2, and N-ary to binary conversion means for producing a decoded binary signal from the N-ary signal as the decoded sequence.
In accordance with another aspect of the present invention, there is provided a transmitting apparatus for sending a signal over a transmission line to a receiving apparatus, comprising binary to N-ary converting means for converting a binary transmit signal into an N-ary signal, the N-ary number being a prime number exceeding 2, as a transmit sequence, encoding means for generating a transmit sequence which includes a nonbinary error correction code, based on the N-ary signal as the information sequence, and multi-level modulation means for multi-level modulating the transmit sequence to sending the modulated transmit sequence to the receiving apparatus.
In accordance with a further aspect the present invention, there is provided a receiving apparatus for receiving a signal from a transmitting apparatus over a transmission line, comprising demodulating mean for demodulating a receive signal from the transmitting apparatus to produce a multi-leveled sequence, the multi-level being a prime number exceeding 2, decoding means for decoding the received sequence by a nonbinary error correction code decoding method to produce an N-ary signal, the N-ary number being a prime number exceeding 2, and N-ary to binary converting means for producing a decoded binary signal from the N-ary signal as the decoded sequence.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description in conjunction with the accompanying drawings wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out this invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.